1. Field of the Invention
The present invention relates to a novel polymeric liquid crystal copolymer compound having a siloxane or oxyalkylene unit in its side chain, a polymeric liquid crystal composition containing such a polymeric liquid crystal copolymer compound, and a liquid crystal device making use of any of these polymeric liquid crystal copolymer compound and polymeric liquid crystal composition.
The present invention also relates to novel polymeric liquid crystal copolymer compound having a siloxane in its main chain, a polymeric liquid crystal composition containing such a polymeric liquid crystal copolymer compound, and a liquid crystal device making use of any of these polymeric liquid crystal copolymer compound and polymeric liquid crystal composition.
The polymeric liquid crystal copolymer compound and the polymeric liquid crystal composition containing the polymeric liquid crystal copolymer compound, according to the present invention, can be used as materials for optoelectronic devices, optical devices and so forth as typified by optical display devices and optical memories.
2. Related Background Art
Liquid crystal devices hitherto available are known to include those making use of a twisted nematic liquid crystal as disclosed in M. Schadt and W. Helfrich, "Voltage Dependent Optical Activity of a Twisted Nematic Liquid Crystal", Applied Physics Letters, Vol. 18, No. 4, published Feb. 15, 1971, pp. 127-128. This twisted nematic crystal, however, has the problem that crosstalk may occur in the timesharing drive that makes use of a matrix electrode structure having an increased picture element density, and hence there has been a limitation on the number of picture elements.
There is also a limitation on its use as a display device because of its slow response and poor visual-field angle characteristics. There are also the problems that it requires a very complicated process to form a thin-film transistor in each picture element and also is accompanied with a difficulty in fabricating a display device having a large area.
As an improvement that can eliminate the disadvantages of liquid crystal devices of such a conventional type, Clark and Lagerwall have proposed to use a liquid crystal device capable of assuming either one of two stable states (i.e. bistability), see Japanese Patent Application Laid-open No. 56-107216 or U.S. Pat. No. 4,367,924.
As a liquid crystal having such a bistability, it is common to use a ferroelectric liquid crystal comprised of a chiral smectic C phase (Sm*C) or H phase (Sm*H). This ferroelectric liquid crystal has spontaneous polarization and hence has a very high response speed and also can achieve the two stable states with memory performance. In addition, it has superior visual-field angle characteristics and hence can be considered suitable as a material for large-area display. In actual fabrication of a liquid crystal cell, however, it is difficult to achieve a single domain over a wide area, and there has been a technical problem in the fabrication of a large-screen display device.
It is also known to use a polymeric liquid crystal as a memory medium.
For example, it includes a thermal write memory disclosed in V. Shibaev, S. Kostromin, N. Plate, S. Iranov, V. Vestrov and I. Yakovlev, "Thermotropic Liquid Crystalline Polymers. 14", Polymer Communications, Vol. 24, pp.364-365.
However, the method disclosed in this publication, which utilizes light scattering in reading, can achieve only a poor contrast and also has the problem that the response speed is lowered as the material has a higher molecule. Hence, this method has not put into practical use.
Japanese Patent Applications Laid-open No. 63-72784, No. 63-99204, No. 63-161005, etc. disclose polymeric liquid crystals having ferroelectric properties.
These polymeric liquid crystals, however, even though they are nematic liquid crystals, or chiral smectic liquid crystals having ferroelectric properties, have so high a viscosity than low-molecular liquid crystals that they have greatly poorer response performance. Now, it is attempted to use a blend of the above polymeric liquid crystal and a low-molecular compound or low-molecular liquid crystal that serves as a viscosity reducing agent. Even with use of such a blended polymeric liquid crystal composition, large-area display may become difficult because of poor film properties required as a polymer or phase separation may occur because of lack of compatibility. Hence, it has been impossible to manufacture good polymeric liquid crystal devices.